The ancient ancestor of SARS-CoV-1 and SARS-CoV-2: what is known about it

The pandemic caused by the SARS-CoV-2 coronavirus has already caused the death of almost 5 million people worldwide. And the number of deaths continues to rise. Over the past 20 years, this is the third epidemic due to coronaviruses. In 2003 and 2012 Humanity has experienced SARS and MERS outbreaks caused by the SARS-CoV-1 virus. But as scientists recently discovered, epidemics provoked by coronaviruses happened long before the 21st century. Presumably one of the oldest occurred about 20 thousand years ago. Its cause was the common ancestor of SARS-CoV-1 and SARS-CoV-2.

Epidemics and mutations of viruses

The human body has been fighting viruses since time immemorial. As a result of this confrontation, mutations occur in the human genome that make the body less vulnerable to a particular pathogen. These changes are transmitted from generation to generation at the genetic level, thereby ensuring the survival of humanity as a species. For example, as a result of such a mutation, the human body can acquire the ability to break down the proteins of a particular virus, thereby protecting itself from death.

But such properties are characteristic not only for humans, but also for the virus. In simple terms, the main goal of any microorganism is to create as many copies of itself as possible. And for this, he must penetrate the cell of other organisms and capture it. If the virus collides with the defense mechanisms of the host cell, it mutates - it acquires features that allow it to bypass the barrier.

But if the human body nevertheless develops resistance to the virus, then this ability is “recorded” in the corresponding gene, and it is already passed on to the next generations. If the altered version of the gene dominates in large groups of people, this may be evidence of a past epidemic and human adaptation to the pathogen that caused the disease.

As for coronaviruses, their abilities to mutations are striking. Over the past 20 years, three types of coronaviruses that previously only infected animals have adapted to infect humans. We are talking about the causative agents of severe respiratory diseases MERS, SARS and COVID-19. Outbreaks of diseases caused by coronaviruses in the past 20 years have shown that pathogens of this family are able not only to mutate, but also to overcome the species barrier. One such coronavirus, known as HCoV-HKU1, crossed the species barrier in the 1950s. But he was clearly not the first of his family to strike a man. Until recently, HCoV-NL63 was considered one of the most ancient coronaviruses, with an estimated age of about 800 years. But how it all began, when the first coronavirus dangerous to humans appeared and how much it has mutated since then - these questions remained unanswered for a long time. But the rapid development of genetics as a science has opened up new opportunities for scientists.

An ancient epidemic of coronavirus

Scientists have been working to determine the estimated age of coronaviruses for a long time. The answer to the question of how long coronaviruses exist on the planet, experts were looking for by studying the genes of coronaviruses. But recently, a group of scientists from the University of Arizona decided to take a fundamentally different approach - to study not the virus itself, but its effect on human DNA.

Even before the COVID-19 pandemic, a group of evolutionary biologists began to study how different viruses affect changes in the human genome. The knowledge gained would help determine the age of many viruses. But when the pandemic hit, scientists decided to apply the same method to see if there were traces of the SARS-CoV-2 ancestor in the human genome. Specialists, using the latest computer analysis methods, compared the genomes of more than 2.5 thousand people from 26 populations from different parts of the world. At the same time, the main attention was paid to genes associated with adaptability to coronaviruses. In DNA samples from representatives of 5 populations of East Asia, the researchers found 42 genes with signs of adaptation to coronavirus. Representatives of other groups did not have this feature. In addition, it turned out that all 42 genes have approximately the same number of mutations. Presumably, these changes occurred relatively quickly and at about the same time.

Based on these data, scientists hypothesized that East Asians in ancient times already experienced an epidemic caused by a coronavirus and were able to adapt to the pathogen. According to scientists, these mutations in the genes occurred about 20-25 thousand years ago. And, most likely, they were formed over several centuries. Scientists have suggested that the virus that caused these mutations is the most ancient common ancestor of the pathogen COVID-19, as well as MERS and SARS.

What does this discovery give

According to scientists, the coronavirus epidemic that swept East Asia more than 20 thousand years ago was quite destructive and left an evolutionary imprint in the DNA of modern people. It is assumed that the ancient coronavirus dominated the territory for many years.

What is happening now is in many ways reminiscent of the epidemic caused by the coronavirus in ancient times. And this suggests that if the pathogen is not stopped by the vaccine, then the disease can accompany humanity for several generations.

This discovery allows not only to determine when there were earlier outbreaks of coronavirus infection, but also to understand the genetic characteristics of SARS-CoV-2 and what changes the pandemic can cause at the genetic level. It is quite possible that a more detailed study of these 42 mutated genes will allow developing mechanisms to control the activity of the pathogen and stop its spread.